This invention relates to a pressure measuring device for process control, capable of easy and speedy correction and with improved measurement accuracy.
In order to use a pressure measuring device always with high accuracy, it is essential to conduct periodical inspection for correction. However, it is a troublesome, time-consuming task to make such inspection manually for each of many pressure measuring devices. In such inspection, it is necessary to apply the atmospheric pressure as a reference pressure to the device and to adjust the device in accordance with the reference pressure. For this purpose, there is known such a device as shown in FIG. 1, for example. In this device, a pipe 1 to carry a measuring object or fluid to be measured is provided with a branch pipe 1a, which is connected with a pressure transducer 3 through a solenoid valve 2. The solenoid valve 2 has a valve opening 2a connected to the pipe 1 side of the branch pipe 1a, an opening 2b connected to the transducer 3 side of the branch pipe 1a, and an opening 2c which opens into the atmosphere. Therefore, the atmosphere may be introduced into the device through the valve opening 2c by operating the valve. In measurement the valve openings 2a and 2b are caused to communicate with each other, while in inspection the communicating direction of the solenoid valve 2 is changed to connect the valve openings 2b and 2c, thereby allowing the atmospheric pressure to be measured by means of the transducer 3.
According to the aforementioned prior art device, if the inspection is repeated quite frequently or the pressure inside the pipe is pretty high, a leakage may be caused in the solenoid valve, leading to an error in the measurement of the fluid pressure. Namely, with the valve openings 2a and 2b connected and the openings 2b and 2c disconnected from each other during the pressure measurement, the fluid will leak out from the pipe through the valve opening 2c to induce a pressure loss between the junction of the pipe 1 and the branch pipe 1a and the valve opening 2b of the solenoid valve 2. In consequence, the fluid pressure inside the pipe 1 will be prevented from being transmitted entire to the pressure transducer 3, thus causing the pressure transducer to produce a wrong measurement result.